You are given six cells marked A, B, C, D, E, and F. Some of these are working and some are not. Design an activity to identify which of them are working. (i) List the items that you require. (ii) Write the procedure that you will follow. (iii) With the items, carry out the activity to identify the cells that are working.
Items required: (1) An LED (Light Emitting Diode) or a small incandescent lamp, (2) Two connecting wires with insulation removed from both ends, (3) A cell holder (optional), (4) The six cells marked A, B, C, D, E, and F that need to be tested.
Procedure: (1) Take one cell at a time from the set of six cells. (2) Connect one wire from the positive terminal of the cell (metal cap) to the longer wire (positive terminal) of the LED. (3) Connect another wire from the negative terminal of the cell (flat metal disc) to the shorter wire (negative terminal) of the LED. (4) Observe if the LED glows. (5) If the LED glows, the cell is working; if not, try reversing the connections. (6) If the LED still does not glow after reversing, the cell is not working. (7) Repeat the same procedure for all six cells A, B, C, D, E, and F. (8) Record your observations in a table.
Expected observations: The cells that make the LED glow when connected properly are working cells. These cells provide sufficient electrical energy to light the LED. The cells that do not make the LED glow even after reversing the connections are not working (dead or exhausted). These cells cannot provide enough electrical energy to light the LED. Record each cell as 'Working' or 'Not Working' based on whether the LED glows when connected to it.
Explanation
(i) The chapter shows in Activity 3.6 (pages 6-8) that a lamp or LED can be used to test if a cell is working. The LED is preferred because it clearly shows when current flows through it. (ii) The chapter explains on page 9 that 'The current passes through the LED only when the positive terminal (longer wire) of the LED is connected to the positive terminal of the battery, and negative terminal (shorter wire) of the LED is connected to the negative terminal of the battery.' This principle is used to test cells. (iii) According to the chapter, an electric cell is 'a portable source of electrical energy' (page 3). A working cell provides electrical energy that can make an LED glow when connected in a complete circuit with correct polarity. A dead cell cannot provide this energy.